Problem 26 - A Complete Resource Book in Chemistry for JEE Main

Question

Which one of the following ions exhibit highest magnetic moment? (a) \(\mathrm{Cu}^{2+}\) (b) \(\mathrm{Ti}^{3+}\) (c) \(\mathrm{Ni}^{2+}\) (d) \(\mathrm{Mn}^{2+}\)

Step-by-Step Solution

Answer

ext{Mn}^{2+} exhibits the highest magnetic moment with 5 unpaired electrons.

Step 1: Understand Magnetic Moment

Magnetic moment depends on the number of unpaired electrons in an ion. More unpaired electrons typically mean a higher magnetic moment.

Step 2: Determine Electron Configurations

Identify the electron configurations for each ion, especially focusing on the d-orbitals where unpaired electrons may be present. - ext{Cu}^{2+}: [Ar] 3d^9 - ext{Ti}^{3+}: [Ar] 3d^1 - ext{Ni}^{2+}: [Ar] 3d^8 - ext{Mn}^{2+}: [Ar] 3d^5

Step 3: Count Unpaired Electrons

Count the number of unpaired electrons in the d-orbitals for each ion: - ext{Cu}^{2+} has 1 unpaired electron. - ext{Ti}^{3+} has 1 unpaired electron. - ext{Ni}^{2+} has 2 unpaired electrons. - ext{Mn}^{2+} has 5 unpaired electrons.

Step 4: Determine Highest Magnetic Moment

The ion with the highest number of unpaired electrons has the highest magnetic moment. Since ext{Mn}^{2+} has 5 unpaired electrons, it exhibits the highest magnetic moment among the given ions.

Key Concepts

Unpaired Electrons

Unpaired electrons play a crucial role in determining the magnetic properties of an ion or an atom. In simple terms, unpaired electrons are those electrons that do not have a partner with opposite spin in their orbital. When electrons are unpaired, they contribute to the magnetic behavior of a substance. More specifically, they create a magnetic moment.

Here’s how it works:

• Electrons have a property called 'spin', which creates a tiny magnetic field. When electrons are paired, their opposite spins cancel each other out.
• However, unpaired electrons remain unmatched, resulting in a net magnetic field.

The more unpaired electrons present, the stronger the magnetic moment. That's why manganese in the Mn\(^{2+}\) ion, with 5 unpaired electrons, has a higher magnetic moment compared to other ions like Cu\(^{2+}\), Ti\(^{3+}\), and Ni\(^{2+}\). Understanding unpaired electrons and their impact helps explain why certain materials are magnetic and others are not.

Electron Configuration

Electron configuration is a way of representing how the electrons are arranged within an atom or ion. This arrangement is critical to understanding unpaired electrons and magnetic properties.

Every electron configuration follows specific rules:

• The Aufbau principle states that electrons fill the lowest energy orbitals first.
• According to Hund’s Rule, electrons will fill an unoccupied orbital before they pair up.
• The Pauli Exclusion Principle reveals that no two electrons in an atom can have the same set of four quantum numbers.

For transition metals, the d-orbitals are of particular interest. Transition metals can have varied oxidation states and changes in electron configuration.For example, the electron configurations of the ions in the exercise are:

• Cu\(^{2+}\): [Ar] 3d\(^9\)
• Ti\(^{3+}\): [Ar] 3d\(^1\)
• Ni\(^{2+}\): [Ar] 3d\(^8\)
• Mn\(^{2+}\): [Ar] 3d\(^5\)

The electron configurations reveal where unpaired electrons are located, influencing magnetic moments. By counting unpaired electrons in these configurations, we can determine their magnetic properties.

Transition Metals

Transition metals are a group of elements located in the d-block of the periodic table. These elements are famous for their complex electron configurations and the ability to form various ionic states.A few fascinating features include:

• They have incomplete d sub-levels that can hold up to 10 electrons.
• Transition metals often exhibit variable oxidation states, meaning they can give up different numbers of d or s electrons when forming ions.
• This versatility leads to diverse chemical properties and colorful compounds.

Transition metals also have a strong influence on magnetic properties due to their unpaired d-electrons. Magnetic moments can vary widely depending on the specific ion's configuration.For example, in transition metal ions like those from the exercise:

• Mn\(^{2+}\), with a 3d\(^5\) configuration, has maximum unpaired electrons, resulting in a high magnetic moment.
• Others, like Ti\(^{3+}\), show fewer unpaired electrons and thus exhibit lower magnetic moments.

Understanding these characteristics equips students to predict and explain the magnetic behaviors of these fascinating elements.